what I need is a first-if formula

[Guest]

Can anyone help me to make a formula?
Column A is row number.
Column B shows raw data.
Column C is where I would like a formula to fill down.
Starting with any row, I am interested in later-row data only if greater by
at least 4 above current-row data. I want to find the FIRST such data. In
particular, I want to display its corresponding row number.

A B C
Row Data Earliest Row No. of Data > or = (Current Row Data+4)
11 14 13 [Row 13 has 19, the next data >= 14+4]
12 16 16 [Row 16 has 20, the next data >= 16+4]
13 19* blank [no further rows have data >= 19+4]
14 13 15 [Row 15 has 17, the next data >= 13+4]
15 17 blank
16 20* blank
17 15 blank
18 14 blank

If no later-rows have data greater than current-row data by at least 4, then
blank.

Many thanks.

 

[Bob Phillips]

=IF(MIN(IF(B$18:$B19>=B18+4,ROW(B$18:$B19)))>0,MIN(IF(B$18:$B19>=B18+4,ROW(B
$18:$B19))),"")

this is an array formula so commit with Ctrl-Shift-Enter